“Sentinels” are those who stand guard, watch over, and look ahead. Today, a new corps of sentinels is emerging across the American landscape to steward and defend the last pristine landscapes from disappearing in a tidal wave of urbanization and land conversion. They fight for clean air, clear water, and the freedom to roam for both people and wildlife. They also play a vital and unheralded role in protecting our national security. The Sentinels tells the diverse stories of the guardians living, working, and training in our “Sentinel Landscapes” — installations recognized by the U.S. Department of Defense for both exemplary ecological value and strategic military importance.